translate C struct char array into D

[Paul Backus]

On Friday, 30 July 2021 at 14:05:58 UTC, workman wrote:
> I get want to define this struct in D:
>
> ```c
> struct test1 {
>     struct test1 *prev;
>     struct test1 *next;
>     size_t v1;
>     size_t v2;
>     size_t v3;
>     char data[];
> };
> ```
>
> ```d
> struct test1 {
>     test1 *prev;
>     test1 *next;
>     size_t v1;
>     size_t v2;
>     size_t v3;
>     char* data;
> };
> ```
>
> when I compare the size, test1.sizeof is 48 and sizeof(struct 
> test1) from C is 40.
>
> Anyone can explain what should I do with this ?
>
> If I use test1 as member of other struct, the total size will 
> not match.

`char data[]` in the C struct is not a pointer, but actually a 
[C99 flexible array member][1], and does not count towards the 
struct's `sizeof`.

D does not have flexible array members, but you can simulate one 
using a struct method:

```d
struct test1 {
     // member variables...

     char* data() {
         return cast(char*) (&this + 1);
     }
}
```

[1]: http://port70.net/~nsz/c/c99/n1256.html#6.7.2.1p16